Spreading center— A linear area where new crust forms where two crustal plates are moving apart, such as along a mid-oceanic ridge. Spreading centers are typically seismically active regions in ocean basins and may be regions of active or frequent volcanism.

Subduction zone—a plate boundary along which one plate of the Earth’s outer shell descends (subducts) at an angle beneath another. A subduction zone is usually marked by a deep trench on the sea floor. An example is the Cascadia Subduction Zone offshore of Washington, Oregon, and northern California. Most tsunamis are generated by subduction-zone-related earthquakes.

Transform boundary—when plates slide past each other creating fault systems along plate margins. Examples include the San Andreas Fault and major faults in Pakistan, Turkey, and along the Jordan River/Dead Sea.